KillerTA

First off it's not my TA, it's my 1986 Cadillac Deville.

From what I understand, failing the NOX test is either due to a bad egr valve or a bad catylitic. Is that right?

I can't remember for sure, but is the diaphram on the egr valve supposed to move up and down when the engine is revved? Mine doesn't. The car runs awesome too, except on the highway at speeds of 55mph and up.

I want to make sure what it is before I start spending unnecessary money on parts.

Thanks!

MentalCaseOne

Why are you asking a bunch of LT1 Cowboys about your Candy A...... errr J/k dude...


High NOX emissions occur when the Temperature in the combustion Chambers is too high.... The EGR when opens up recirculates a controlled amouth of exhaust gases back into the combustion chambers... this Exhaust lowers the combustion chambers temperatures....


So to Answer your question... yes A faulty EGR can increase the
amount of NOX emissions in your exhaust...

Sometimes the EGR is working Great and yet the NoX are high.. This could be due to a clogged EGR passages.. Your Cat can also be the reason why you have High emissions... but since you mentioned that your EGR is not moving up and down.. I am almost positive thats a good starting point...

It could be as simple as a torn vacum hose that feeds the EGR or if its electronic it could get more complicated.

good luck

Marvin

Injuneer

High NOx can also be the result of running "lean". In that case, you would pass easilly on HC and CO. How did those look?

MentalCaseOne

Dang!! Injuneer beat me to it...

I left out that part... when I came back to edit my post he had already posted his.....

Whats the Oxygen content and the Hydrocarbons content???



Low in Hydrocarbon and High in Oxygen is a good tell tale that you runnin lean...

Marvin

2MCHPSI

Some times excessive carbon buildup can cause high temps. I alwyas hooked up a vacuum hose to the intake and slowly sucked in water to "steam clean" the pistons. I really do not liek to use heavy detergents liek Gm top engine cleaner or Seafoam. Just be careful not to unduce too much wate, which could bend a valve.. A small diameter hose and 2000 rpms should do the trick. It has fixed many NOX emmisoned cars I worked on with higher mileage

KillerTA

Thanks for all the help guys!

Here are my readings:

HC--0.5959 grams/mile Limit 2.0000

CO--8.7801 grams/mile Limit 30.0000

NOx--3.9333 grams/mile Limit 3.0000


On the NOx graph, there wer spikes and low points all over the chart.

KillerTA

Here we are, 2 years later, and I have nearly the exact same readings again

Last time I had the catalytic converter replaced and it passed. Do you think that could be the problem again

The first time I went (for this year), the egr vacuum hose was off and the NOx was 3.800 and I went again today with it hooked up and it is 4.8572 Coincindence?

HC--.6692 limit 2.000
CO-- 2.1944 limit 30.000
NOx-- 4.8572 limit 3.000

sleeper94z28

i used to work at emissions place and saw those kinda readings alot on the old caddys. first thing is make sure they do the test with the AC off. Cadillac acually put a service bullitin out that siad that could cause high NoX. NoX is caused by high combustion chamber temps which can come from a number of different sources.

1.Carbon build up: carbon build up on the piston or head causes hot spots that raises CC temps and cause detonation.
Fix: get some seafoam from the auto parts store, pour it SLOWLY into the brake booster line while someone holds the throttle down at about 2000-2500 RPM, this should beakup some of that carbon.
2. Detonation: detonation or preignition also causes high NoX
Fix: Put some high octane fuel (93) and drive around to make sure you run it through the fuel system and make sure the plugs are the right temp. you could even go a heat range lower and trade some HC for NoX (usally HC and NoX have an inverse relationship, ie: one goes up and the other goes down
3. Coolant temp: make sure the car is not running hot and has good uncontaminated coolant, also check the thermostat to make sure its not sticking. you can also try using this stuff called "water wetter" to bring coolant temps down.

oh yeah make sure you drive the car for at least 30-45 min after using Seafoam before getting it tested or your results will be worse but the results will be best when tested the same day you used the product

KillerTA

If I went a heat range lower with plugs, would that make enough of a difference that the car would pass?

sleeper94z28

there is no real way to tell without takin a look at the car but, i just threw out some suggestions. Seafoam seems to be the most consistant fix in my experience. remember if you do go with a lower heat range its very possible that your HC will go up. im sure your fed up with car not passing emissions so my opinion is that you flush the cooling system, fill the car up with premium gas, drive around for about 10 miles, use the seafoam, drive around for another 30 min and go get it inspected. i can almost guarantee it will pass.
when i worked at the station and we had a car come in that barely failed, i would tell them that we could do a fuel injection service to the vehicle for 50 bucks to get it to pass. so then id run down to the store get a bottle of seafoam for like 8 bucks, do the service, let the car run for a while, hook it up to the machine and all the gas levels would be greatly reduced, HC CO and NoX.plus after using that stuff you will notice a big improvment in drivability. hope this helps, let me know

sleeper94z28

oh yeah to check to see if the egr is working push the diaphram out while the engine is idleing, if it trys to die then its not clogged up. also check the hose for vacuum, just in case its pinched or clogged